1. Field of Invention
This invention relates generally to the field of piercing, using very fine filaments or piercing tools and to the support of the filaments during the friction-flow piercing process. The invention further cites a testing apparatus and method that relies on the cited piercing method for determining the moisture content of strata in a semi permeable dielectric solid 17.
2. Background of the Invention
The method described and reduced to practice herein, is uniquely useful and practical because it may be applied to fully assembled and cured parent material. It may be applied even while the equipment is in place and running. In addition, the electrical properties are recorded and may be compared with the depth of the filament in real time so that a conductivity profile of the solid thickness is created
This invention is a novel means of supporting an extremely thin and long (high aspect ratio) piercing rod so that it does not buckle under the pressure of a friction-flow piercing operation. The cited piercing method is applied to a test apparatus for testing sub-surface saturation of dielectric solids that are being permeated by conductive fluids. One particular application would be testing of fiberglass (FRP) laminates in industrial chemical services.
The current invention relies on a friction piercing method using a rapidly rotating metallic filament to pierce through a meltable solid substrate 15. The tip of the piercing tool gets very hot from friction, liquefying the solid and causing it to flow along the filament creating a path for the advancement of the filament. No specific chip path is required with friction-flow piercing. The liquefied material flows out along the rotating piercing means. Once the rotation stops, the piercing means is either withdrawn or the liquefied material solidifies, sealing it in place. Since the filament is extremely thin and is inserted without pre-drilling, and if it is constructed from a metal that is chosen for excellent corrosion resistance, insertion will not degrade the substrate and filament can be used as a conductor to allow testing of substrates for electrical properties throughout the remainder of its life. Testing therefore, can be continuous during piercing and on-going after the installation.
Fiberglass (FRP) is notoriously difficult to test by common conventional means because it is highly irregular, full of anomalies, non-magnetic and normally non-conductive. The major testing companies do not attempt to test industrial FRP. There are ways, practiced by the inventor and other specialists in the field to get a reasonably accurate overall thickness measurement, but FRP saturates and often breaks down internally without losing overall thickness.
This testing method allows non-destructive detection of saturation within dielectric solids, and has many other known uses as well. The inventor believes that this method will make Industrial FRP safer and more reliable to use, and may contribute positively to other industries.
The method is simple and field practical and installation takes only few minutes using relatively inexpensive raw materials and installation equipment. Once inserted, the filament may be sealed in place making them extremely robust. The process is essentially non-destructive, and if the filament remains in the laminate and is sealed in place 20, with an end exposed for electrical contact 21, it becomes a permanent test site to detect changes in electrical resistance of the dielectric material 15 by measuring the impedance between the piercing means 1 and the conductive material 18 on the opposing surface 17. This assumes that the conductive material is either earth grounded or shares a direct electrical connection with the meter 11.
In the preferred embodiment, the filament is about 0.01″ diameter, which is too small to cause significant structural interruption in most applications. It is important that the filament is as thin as possible, and that it is self-pierced into the surface, remaining in place to reduce the possibility of escapement of process fluids or gasses during or after the test.
It is understood that the piercing means may be made from but not limited to, tantalum, tungsten, steel, graphite, carbon, bonded carbides of alloys, or coated combinations thereof. Under some circumstances, it may be desirable to coat the length of the filament with a non-conductive coating so electrical measurements originate only from the piercing end of the filament. Coatings must be abrasive, heat and corrosion resistant and may include, but are not limited to ceramic or glass.
The invention teaches a unique means for supporting a very thin piercing member. By encapsulating the slender piercing rod in a low melt temperature plastic sheath such as styrene, a combination is produced that is stiff enough to pierce a hole with depth more than 300 times the diameter of the piercing means without relying on elaborate mechanical external support. The plastic simply melts away 19 from friction at the surface as the piercing tool enters the substrate 15. This method has proven extremely practical and is expected to be valuable to other applications as well.